Some four-wheel drive vehicles have a lateral acceleration sensor that measures the lateral acceleration acting on the four-wheel drive vehicle, and a drive power distribution control device that controls the distribution of drive power transmitted to the front wheels and rear wheels based on the measured lateral acceleration. This type of four-wheel drive vehicle includes sensor fault detection means for detecting faults in the lateral acceleration sensor due to a breakdown, or similar. When the sensor fault detection means detects a breakdown (fault), a predetermined fail safe operation is carried out (see for example, Japanese Patent Publication No. H7-40040).
However, conventionally, in the time from occurrence of an actual sensor breakdown until the sensor breakdown is detected (usually about 10 seconds), the drive power distribution ratio and so on are calculated based on faulty measurement values. Therefore, there was a danger of altered behavior of the vehicle due to inappropriate drive power distribution, and reduced running stability. Also, after a sensor breakdown is detected a fail safe operation is started. Therefore, if for example during the fail safe operation drive power distribution to the rear wheels is stopped, distribution of drive power to the rear wheels is suddenly stopped from an inappropriate state, so there was the danger that the vehicle behavior immediately after starting the fail safe operation would be unstable.